Subsurface Oceans

Evidence of Subsurface Oceans:Original Article
“1979–2000 — Using data from the Voyager and Galileo spacecraft, scientists gather strong evidence of an ocean beneath the icy crust of Europa; Galileo data indicate oceans within Ganymede and Callisto.”

“The interiors of Io, Europa, and Ganymede have a layered structure (as does Earth). Io has a core, and a mantle of at least partially molten rock, topped by a crust of solid rock coated with sulfur compounds. Europa and Ganymede each have an iron-rich core; a rock envelope around the core; a thick, soft ice layer; and a thin crust of impure water ice. Layering at Callisto is less well defined and appears to be mainly a mixture of ice and rock. Like Europa, Ganymede and Callisto have oceans, but they are deeper and less accessible than Europa’s, and sandwiched between ice layers rather than in contact with their mantles”

“Cassini’s detection of large tides on Titan leads to the almost inescapable conclusion that there is a hidden ocean at depth,” said Luciano Iess, the paper’s lead author and a Cassini team member at the Sapienza University of Rome, Italy. “The search for water is an important goal in solar system exploration, and now we’ve spotted another place where it is abundant.”

“Earlier models had suggested an ocean exists on Triton, but they were quite simplistic. Saswata Hier-Majumder of the University of Maryland in College Park, and his student Jodi Gaeman, have now developed a more detailed model that considers both radioactive decay of core minerals and the orbital interactions that would have heated the moon.”

“Beyond the asteroid belt, water ice is abundant. It is a minor component of Jupiter’s moon Europa, but constitutes almost half the mass of Jupiter’s moons Ganymede and Callisto and Saturn’s moon Titan. It is the dominant, or at least key, constituent of the intermediate-sized moons of Saturn (e.g., Enceladus), the moons of Uranus, Neptune’s moon Triton, and the Kuiper belt object Pluto and its moon Chiron.”

“But there must have been water, and plenty of it, in Mars’s past. That is evident from the massive outflow channels that are found, mostly, in the northern lowlands. The intensity of the floods that carved these channels was tremendous, perhaps reaching discharge rates as high as 10,000 times that at which the Mississippi, when flooded, pours into the Gulf of Mexico.

What caused these giant floods? Was it a climate change, perhaps brought about by a change in Mars’s orbit? Or was the planet’s own internal heat responsible? And, whatever mechanism caused the floods in the first place, where has all that water gone? Was it absorbed into the ground where it remains today, frozen? Or did it dissipate into the Martian atmosphere, where it was subsequently lost to space? No-one knows for certain the answers to these questions.”

“And if these vexing problems weren’t enough, recent images from MOC reveal a startling new puzzle. In nearly a dozen different locations on Mars – all of them far from the equator – there are signs that water has been seeping out of the walls of valleys and craters, forming small gullies. Some scientists speculate that this activity is very recent, perhaps occurring within the past 10 years; others say 10 million years is more likely.

Yet many aspects of these seepage gullies defy common sense. “They sure look like water-worn features,” says Mike Carr, “but they seem to contradict what we know about the stability of water.” They occur not only in the coldest regions on Mars, but on slopes facing away from the Sun, where the temperature rarely gets above minus 50 degrees Centigrade. Yet the water appears to be seeping out from only 100 meters below the surface, a depth at which scientists previously believed Mars’s crust to be frozen solid. Scientists are busily working to devise an explanation for this phenomenon.

Above: Martian gullies in Newton Crater. Scientists hypothesize that liquid water burst out from underground, eroded the gullies, and pooled at the bottom of this crater as it froze and evaporated.”